Broadband Dielectric Spectroscopy Studies of Nafion

David Walter Rhoades


In light of available literature regarding Nafion® materials it is apparent that an information gap exists between the current state of understanding of Nafion® relaxations and the dielectric behavior of these materials. Although the currently available dielectric relaxation data is accurate it is very limited in its scope--specifically in-depth broadband analyses are not available. As a result very little information is available regarding the dependence of the relaxation processes on frequency and temperature. This presents an important opportunity for the exploration of the dielectric broadband relaxation behavior of Nafion® materials. The primary intent of this research is to quantify the dependence of the α and β relaxations on frequency and temperature from 10 2 -10 -6 Hz and -130 to 200°C by using the VFT equation in conjunction with the fragility index m . Four particular systems are analyzed: the non-ionic precursor form of Nafion®, a chemically crosslinked form of Nafion, the acid form of Nafion® and a chemically degraded acid of Nafion®. Specifically for the acid form special attention is paid to the impact of thermal history and film preconditioning on these relaxation processes. This later step is frequently overlooked but as we confirm it is crucial for reliable and repeatable BDS data. For all forms of Nafion® studied here τ 0 >> 10 -14 ; however, τ 0 typically equals 10 -14 for most polymers. Higher τ 0 and m values correlate with greater restriction imposed on the side chains via the physical or chemical cross-link which is transferred to the segmental motions of the backbone.